I don't know any German equivalent but I wouldn't translate it literally. Grasp the idea and phrase it your own, in respect to your context. If another idiom fits in your context take that, e.g. "Wo kein Kläger, da kein Richter" (If nobody is complaining it can't be so worse).
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Em1Apr 4 '13 at 12:25

@Em1: I'd translate it, "If nobody is complaining it can't be judged." But the correct version of your expresson is, "if nobody is complaining it can't be so BAD."
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Tom AuSep 12 '13 at 0:08

In parts of Austria we say: "Hilft nix, schadet nix" (so literally: it doesn't help, but it also doesn't harm you), but thats not quite the same as your idiom.
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kappadokyMar 9 at 7:38

As far as I understand the English expression "no harm, no foul" it is used colloquial rather than in standard English (but I am not a native English speaker). Then a frequently used colloquial analogue in German would be

"Ach was, ist doch nichts passiert."

In this expression the interjection "Ach was" makes the accident light, and also implies an apology. The second part "...ist doch nichts passiert" corresponds to "no harm".

The German expression "Wo kein Kläger, da kein Richter," literally means, "Where there is no plaintiff, there is no judge," and is probably the closest. In the German idiom, the emphasis is on the PERSONS doing the complaining or judging, as opposed to whether the ACTS can be complained about (harm) or judged (foul)

The meaning is related, but not the same. "Wo kein Kläger, da kein Richter" will be used when there is actual harm and actual foul, but nobody is complaining. For example a son stealing the father's money, but the father not calling the police to avoid the own son going to jail.
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gnasher729Mar 9 at 0:36

@gnasher729: I said that "Wo kein Kläger, da kein Richter" is "probably the closest" to the English idiom, not that they were the same. Often, there are no literal translations from one language to another, only reasonable "equivalents."
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Tom AuMar 9 at 13:03

No, there is no similar figure of speach in German. Even the rule in soccer that comes closest to the meaning of the basket ball rule has no good name in German: the name "Vorteil" (advantage) misses the point (because we lack a better word, I assume).